Jeep Straight Six Stroker Build: Big Power on a Budget

The Jeep straight six is one of the greatest engines of all time. But that doesn't mean it can't be improved. Newcomer Racing shows us how to put together a big power, naturally aspirated stroker 4.0 Jeep engine without spending big coin. The basic recipe is to use the block and connecting rods from a 4.0 Jeep with the longer stroke crank from a 4.2. Of course, there's a lot more too it than that, and we'll spell it out there.

Also, don't forget to scroll down to the end of this post. Newcomer recently followed up with pics of the engine installed in a Cherokee and even results of a tuning session on a chassis dyno.

And if you want to get one of your own, check out

Although not complete, here's a partial parts list. (Note: For the stock replacement components they may not be the exact same brand Newcomer Racing uses.):

Sealed Power pistons

Hydraulic lifters

Valve Springs

Stamped Steel Rocker Arm Kit

Jeep 4.0 block
The newer NVH "Noise Vibration and Harshness" blocks seem to work best because they are a beefier casting and use a crank girdle.
Sealed Pro Pistons
Sealed Pro pistons dropped into the block.
Jeep 4.0 Stroker Crankshaft
The crank is from a 4.2 liter Jeep engine. The 4.2 has a longer 3.895 inch stroke versus the 4.0's 3.414.
Jeep NVH block stud girdle
The NVH block from newer Jeeps uses a stud girdle for extra strength. For a stroker build you may need to add washers to create a little more space for the extra stroke.
Jeep connecting rods Sealed Power pistons
Sealed Power pistons go onto the stock connecting rods.
Jeep 4.0 Bullet Racing Cam
The cam is a hydraulic flat tappet from Bullet Racing Cams.
Jeep 4.0 Cylinder Heads
The head we will be using is a stock cast iron unit with some port work done to help flow.
Jeep 4.0 engine build
Stock valve springs will control the valves.
Jeep 4.0 intake manifold
The intake and exhaust flow off the same side of the cylinder head.
Jeep stroker 4.0 on the dyno
On the engine dyno.
Jeep stroker 4.0 dyno results
Dyno results.
Jeep stroker engine
The stroker engine back into its home in the Cherokee.
Jeep Cherokee
Jeep Chassis Dyno Results
Dyno results with a little tuning using the stock efi and fuel injection once the engine is in the Cherokee.

7 Responses

  1. How much for the 4.0 striker? Where is your pricing??
    • jeff
      This build complete from intake to oil pan is right around $5,000 right now from Newcomer Racing. But every build is different. You can reach them at Thanks
  2. Please do something for those of us saddled with AMC 2.5l I4. Come on and help fan out!!!! Something to get us super excited! Okay we challenge you to put together a 250 horse 2.5!!!!!!!!!!! From a fan in need of power!!!!!!!!LOL Ray Kilsby
  3. I Worked for AMC/JEEP/ CHRYSLER engineering from 1976 to 2001, now retired. I was Engr in charge of airflow development. I'm the person that developed the 4cylinder JEEP & The JEEP 4.0L Cyl heads. (This is not a joke!) Back in 1993 I developed a 4.0L JEEP engine for drag racing, NHRA Competition Eliminator. It was an E/EA for Garth Hill and Charlie Williams. Set National record in 1996 at 8.60ET/ best speed 150.90 MPH, very quick & fast. Runner Up at the 1995 U.S.Nationals (INDY), Foul start (should have won). Currently helping Bob Salemi from Rhode Island, he runs a stocker 92 Jeep Comanche in NHRA STOCK CLASS, R/SA. Set Record at 12.95, runs off a 14.05 index, #1 qualifier Epping NH 2014, 12.879 ET/ 100.8 MPH, Best ET 2019 12.792/ 102.44 MPH, worked on valve train Harmonics, found more power. BEST stock cast head from production is either 1992 or 93 castings, New Haven foundry look for NH cast on top between rocker pedestals. Small Exh port heads no good for power, Made for emmisions, Faster CAT light off time so PRE-CATS not necessary (Cost factor). Just want to let you know if I can help you on anything related to 4 cyl or 4.0L Jeeps let me know. I also do Engine Computer modeling, engine combination, cam selection, intake manifold tuning, header tuning, etc. All variables investigated. Nice job! I enjoy your DYNO testing on the 4.0L stroker project. Later, Rick
    • jeff
      Very cool. Thanks!
      • I won't drop anymore comments after this, promise! There are still two YouTube video's showing our E/EA comp elim 32 bataam Altered. One from 1995 U.S. Nationals at INDY Final Round. The other from SPRING NATIONS, Columbus, Ohio 1997. Titled: 1995 NHRA U.S. NATIONALS AT INDIANAPOLIS RACEWAY PARK (have to go to time 1:48:18) 2nd Video was a middle round from the Spring Nationals at Columbus, Ohio in 1997. Both cars run same class E/EA , Yellow car was Jerry Arnold having a FORD inline 6cyl 250in3, Garth Hill drives our 4.0L 248in3 Jeep, both engines have 3 500cfm two barrels, & Automatics. Titled: NHRA COMPETITION ELIMINATOR PPV (Time: the second pair of cars to run, right after John Lingenfelter's OLDS dragster) Hope you like the video's! NO more e-mails!
  4. want to talk about 4.7 jeep engine.

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